The present invention relates to a light barrier system, particularly for automatic doors, having an electric light emitter arrangement as well as an electric light receiver arrangement that interacts with the light emitter arrangement and generates an electric signal when the light path of the light barrier is interrupted or cleared.
For automatic doors, as a rule, several light barrier arrangements are provided in order to, on the one hand, be able to monitor the area directly in the plane of the door opening and, on the other hand, also monitor the areas in front of and behind this plane. The light barrier arrangements are combined with electronic control systems which actuate the door drive or the door drives as a function of whether one light barrier or several light barriers are interrupted or not.
In known light barrier systems, in addition to the lines for the electrical power supply, separate control lines are also required for each light barrier arrangement, so that as a rule, four connections exist for each light barrier arrangement.
This makes the cabling problematic, particularly when many light barrier arrangements are provided at one door. Also, it is disadvantageous that the miniaturization of electronic control systems that is theoretically possible cannot be carried out or are difficult to be carried out because of the many required cable connections. This is particularly true when the light barrier systems must also be able to be checked with respect to short circuits and/or line breakages, because for this purpose, the number of connections per light barrier arrangement that is high in any event, up to now, had to be increased even more.
It is therefore an objective of the present invention to provide a light barrier system that, despite only minimal expenditures for the cabling, can be monitored with respect to short-circuits as well as line breakages.
This and other objectives is achieved in the present invention by providing a radiant energy barrier system having a radiant energy receiver and a radiant energy emitter, in which an electric signal is generated when an energy path between the emitter and receiver is interrupted or cleared, with a two-terminal network. The system includes a power source for providing power to the system, at least one power supply line connecting the source to the system. The emitter and receiver are interconnected in the network. The network has a potential difference between the two terminals that are connected to the power source that is changed by the interruption or clearing of the energy path. A monitoring means reacts to the potential difference and is connected away from the barrier system at the power supply line.
The invention is therefore based on the general idea of developing the radiant energy barrier arrangement as an active or passive two-terminal network that, in the case of an undisturbed operation, switches over between two conditions that are characterized by a different potential drop or by different potential differences at the two-terminal network. One of the different potential drops (or differences) occurs when the light path is cleared and the other occurs when the light path is interrupted. Should a potential drop or difference occur that deviates from the two values that are characteristic of a normal operation, a system disturbance must exist, such as a short circuit or a line breakage.
A special advantage of the invention is the fact that the potential drop or electric quantities that are associated with it can very easily be tapped away from the light barrier arrangement at one or both power supply lines of the light barrier system. Accordingly, the light barrier system according to the invention requires only two electric power supply lines, but no additional control or monitoring lines with assigned cables. Even one single supply line per light barrier arrangement may also be sufficient if, for example, for the zero potential, a collective connection is used for all external apparatuses and/or light barrier systems of one door control system or the like.
According to a particularly preferred embodiment of the invention, it is provided that the two-terminal network is connected in series with at least one precision resistor arranged in a supply line and the monitoring circuit is connected with an input between the resistor and the two-terminal network.
In this particularly preferred embodiment, the monitoring circuit can evaluate the potential drop at the precision resistor or the electric level as the input signal. When the operation of the light barrier arrangement is undisturbed, only two values for the potential drop or level can occur, whereas in the case of a line breakage or of a short circuit, an extremely low or an extremely high potential drop or extremely high or extremely low levels are measured.
In a manner that is particularly simple with respect to circuit technology in certain preferred embodiments, the two-terminal network with a potential drop or difference that changes according to the condition of the light path of the light barrier, may be implemented by using a digital output of a circuit part that is arranged as a part of the network, which when the light path is cleared or interrupted, is located at different voltage levels. One terminal of the two-terminal network, via a resistor, is connected with this output. In order to be able to differentiate between the conditions of the light path, each light barrier arrangement basically requires one circuit part, the output of which, in a corresponding way, alternates between two conditions. According to the present invention, it is therefore sufficient to connect this type of output with one terminal, i.e., with one supply line of the two-terminal network formed by the light barrier arrangement, via a resistor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.